1. Field of the Invention
The present invention relates to an auto-darkening filter, and more particularly to an auto-darkening filter of a welding shield.
2. Description of Related Art
A welding helmet is a type of headgear. A user who performs welding fabrication process to a work piece should wear the welding helmet to protect the face, eyes and neck from flash burn, ultraviolet light, sparks, heat and toxic welding gas.
Auto-darkening filter is an electro-optical device equipped on the welding helmet. The auto-darkening filter operates in a bright state until an optical sensor thereon detects welding arc. In the bright state, the auto-darkening filter allows the user to retain full vision to see the work piece and surroundings. When the optical sensor detects a light source (such as welding arc) with brightness higher than a threshold, the auto-darkening filter is switched to a dark state to shade the user's eyes from the welding arc.
After the welding fabrication process is accomplished, the user may use a grinding machine to grind the work piece. Sparks are often produced from contact position between the grinding machine and the work piece. However, during the grinding process, whole brightness including the sparks and surroundings sensed by the auto-darkening filter would sometimes be higher than the threshold. This can make it difficult to complete the grinding process properly because the user would lose vision when the auto-darkening filter is being darkened.